This term is used to describe a group of anatomical deformities which lead to respiratory compromise in brachycephalic breeds. These deformities include stenotic nares, laryngeal deformities and hypoplastic trachea. The clinical signs are of upper airway obstruction, and secondary complications; concurrent conditions such as laryngeal oedema and bronchopneumonia can occur in severely affected dogs.

Bronchiectasis

This is a dilatation of the bronchi, occurring as a complication of chronic bronchitis or bronchopenumonia. The changes are irreversible once present.

Bronchial cartilage hypoplasia

This condition presents early in life, usually causing severe respiratory distress.

Chylothorax (see plate 30)

This condition is quite common. Clinical signs are the same as for other pleural effusions, dyspnoea being especially common.

Collapsed trachea

This condition can occur in young dogs with a severe form of the condition, or later in life in those less severely affected. Clinical signs include coughing and inspiratory stridor. A characteristic ‘goose-honk’ cough may be heard.

Feline asthma

Also known as feline bronchitis, allergic bronchitis. This condition can present with mild, chronic or acute severe signs. Coughing and dyspnoea are seen.

Hypoplastic trachea

This is part of the brachycephalic upper airway syndrome.

Laryngeal paralysis

This condition is usually idiopathic, but may be related to generalised myopathies or neuropathies. Stridor, aggravated by excitement and exercise, is the main clinical sign, although severe cases may progress to cyanosis and collapse.

Lung lobe torsion

This rare condition is more common in large, deep-chested breeds. Presenting signs include dyspnoea and pleural effusion. There may be an accompanying chylothorax.

In this condition, the mechanism for removing mucus from the airways is defective, leading to respiratory infections. Other conditions associated with defective ciliary function include loss of hearing and loss of sperm motility, with consequent infertility.

Pneumonia due to Pneumocystis carinii

Pneumocystis carinii is a protozoal organism, infection with which may result in pneumonia in the presence of immunosurpression (see also under Haematological/Immunological conditions).

Pulmonary interstitial fibrosis

This condition may be secondary to chronic respiratory disease, leading to the replacement of alveolar walls and lung interstitium with fibrous tissue. This leads to a reduced inspiratory capacity. Clinical signs of cough and exercise intolerance progress slowly.

Spontaneous thymic haemorrhage

This may occur in young dogs at the time of thymic involution, and may be fatal.